A wheel bearing apparatus that supports a vehicle wheel has a rotatably supported wheel hub that mounts a wheel. The wheel hub is supported via a rolling bearing. The apparatus is for driving wheels and driven wheels. For structural reasons, the inner ring rotation type is used for driving wheels and both inner ring rotation type and outer ring rotation type are used for driven wheels. In order to have a desirable bearing rigidity, durability for miss-alignments and superiority in fuel consumption, double row angular contact ball bearings with a small rotational torque have been used. On the other hand, double row tapered roller bearings have been used for heavy duty vehicles such as off-road cars or trucks.
Since the wheel bearing apparatus is usually arranged at a place liable to be splashed by muddy water etc., a sealing apparatus is arranged between an outer member and an inner member to seal the space between them. Generally, a sealing member of the sealing apparatus has sealing lips. The sealing member is mounted on the outer member forming a secured side member. The sealing lips slidingly contact the outer circumferential surface of the inner member.
One example of such a wheel bearing apparatus is shown in FIG. 3. The wheel bearing apparatus 50 includes an outer member (outer ring member) 51 immovably secured on a body of a vehicle. An inner member (inner ring member) 52 is rotatably mounted on the outer member, via balls (not shown). A wheel (not shown) is mounted on the inner member 52 rotatably relative to the body of the vehicle. Since the wheel bearing apparatus 50 is arranged at a place that is liable to be splashed by muddy water etc., a sealing apparatus is arranged between the inner member 52 and the outer member 51.
The sealing apparatus includes a sealing member 53 fit into the inner circumference of the end of the outer member 51. A metal annulus 57 is fit onto a base 56 of a wheel mounting flange 55 of a wheel hub 54. The sealing member 53 includes an elastic sealing member 58 with an annular configuration. A metal core 59 supports the elastic sealing member 58. The elastic sealing member 58 includes three annular sealing lips 58a, 58b 58c. The sealing lip 58a, 58b and 58c are formed so that they can be arranged, respectively, near a flange surface 54a of the wheel hub 54, a curved surface 54b of the wheel hub 54, and an outer circumference 54c of the shoulder portion of the wheel hub 54.
The metal annulus 57 has a fitting portion 57a fit onto an outer circumference 54c of the shoulder of the wheel hub 54. A flange portion 57b is arranged to be in close contact with a flange surface 54a of the wheel hub 54. A seal mounting portion 57c, formed with a crank shaped cross-section, extends in a direction away from the flange surface 54a of the wheel hub 54. A non-contact sealing portion 57d axially extends along a chamfered portion 51a of the outer member 51. A gap or clearance “C” between the inner side surface of the non-contact sealing portion 57d and the chamfered portion 51a and the outer circumference 51b of the outer member 51 is set to have a very narrow dimension.
An elastic member 60 is mounted in a sealing space, formed between the flange surface 54a and the seal mounting portion 57c, after the fitting portion 57a of the metal annulus 57 is fit onto the outer circumference of the shoulder portion of the wheel hub 54. Thus, the flange portion 57b of the metal annulus 57 is in close contact with the flange surface 54a of the wheel hub 54. In addition, a labyrinth seal is formed by the clearance “C” between the inner side surface of the non-contact sealing portion 57d and the chamfered portion 51a and the outer circumference 51b of the outer member 51.
The elastic member 60 mounted in the sealing space can prevent the entry of muddy water etc. into the contacting portion between the metal annulus 57 and the wheel hub 54. The labyrinth seal, formed by the gap or clearance “C” between the inner side surface of the non-contact sealing portion 57d and the chamfered portion 51a and the outer circumference 51b of the outer member 51, can prevent the entry of muddy water etc. into the sliding contact portion between the sealing member 53 and the metal annulus 57. Patent Document 1: Japanese Laid-open Patent Publication No. 291485/2005
However, one problem of the prior art is that once muddy water etc. has entered through the slight gap or clearance “C”, it is difficult to discharge it to the outside of the bearing apparatus. Accordingly, the muddy water etc. dwells on the elastic sealing member 58 adhering to the slide-contacting surface of the sealing lip 58a. Thus, this causes abnormal wear. Accordingly, it is difficult to provide a wheel bearing apparatus that can improve the sealability of the seal and maintain a desirable bearing performance for a long term.